In the subterranean well drilling and completion art, tests are performed on formations intersected by a wellbore. Such tests can be performed in order to determine geological or other physical properties of the formation and fluids contained therein. For example, parameters such as permeability, porosity, fluid resistivity, temperature, pressure, and bubble point may be determined. These and other characteristics of the formation and fluid contained therein may be determined by performing tests on the formation before the well is completed and placed in service.
One type of testing procedure measures the composition of the formation fluids by obtaining a fluid sample from the formation. In order to obtain a representative sample, the sample is preserved as it exists within the formation. A general sampling procedure involves lowering a sample chamber into the wellbore, obtaining a sample, and retrieving the sample in the sampling chamber to the surface for analysis. It has been found, however, that as the fluid sample is retrieved to the surface, the temperature and pressure of the fluid sample can decrease. This change in properties can cause the fluid sample to approach or reach saturation pressure creating the possibility of phase separation, which can result in asphaltene deposition and/or flashing of entrained gasses present in the fluid sample. Once such a process occurs, the resulting phase separation may be irreversible so that a representative sample cannot be obtained without re-running the procedure to take an additional sample.